The present invention is directed to a high-powered firearm cartridge of unique profile which makes it especially adaptable for use in a short-action firearm having a mating chamber and bolt assembly.
More particularly, the cartridge has unique length and diametric relationships which enable propellants to be burned more quickly and completely, thereby producing more energy and muzzle velocity for any given powder capacity than is possible with most previous cartridges having the same powder capacity.
The present invention also provides a unique cartridge configuration which enables the use of a short, fat cartridge in a short-action firearm while assuring smooth and reliable feeding and chambering of the cartridges from a magazine.
In an article which I published in the January 1996 issue of Shooting Times magazine, I discussed the advantages of certain cartridges previously developed by Ackley, Mashburn, Palmisano and Pindell for improved velocity and accuracy. I also mentioned in the article that I had developed a high-power cartridge by modifying a 1908 Westley-Richards cartridge so as to have a unique, short, fat profile which could, for the first time, compatibly combine high velocity, accuracy and power with the compact, well-balanced and lightweight characteristics of a short-action firearm.
However, I had not at that time recognized the problem of permanent lengthwise cartridge case deformation caused by the severely-rebated, small-diameter rim and resultant large unsupported area of the rear wall of the much larger-diameter Westley-Richards cartridge case. Such cartridge case, when modified as described above to produce the propellant-burning characteristics and internal gas pressure curve profile discussed hereafter, proved incapable of withstanding internal gas pressures of at least about 50,000 psi without permanent rearward deformation of the unsupported area of the rear wall of the case, causing the bolt to bind within the extractor groove.
Also, at that time I had not recognized the importance of at specific maximum limit on the length-to-diameter ratio of a cartridge case necessary to produce the desired propellant-burning characteristics and internal gas pressure curve profile discussed hereafter.
A firearm cartridge is provided having a projectile and an elongate tubular case capable of withstanding internal gas pressures of at least about 50,000 psi. The case has a first end defining a substantially circular base with an annular rim and a second end defining a mouth for insertably receiving the projectile. The case is also characterized by a first portion of substantially cylindrical shape adjacent to the first end and a second portion of a narrower substantially cylindrical shape adjacent to the second end with a frusto-conical shoulder portion interconnecting the first and second portions. The overall length has a ratio to the outer case diameter at a location 1.25 inches from the first end of no more than about 4.2. The rim has an outer diameter substantially no less than the outer case diameter at this same location. Such a wide rim at the base of the cartridge prevents the permanent lengthwise deformation of the cartridge case experienced with the rebated rim structure of the Westley-Richards cartridge, while also assuring smooth and reliable feeding of the cartridge despite its unusual profile.
To produce the desired propellant-burning characteristics and internal gas pressure curve profile discussed hereafter, the outer case diameter at the foregoing location is preferably at least about 0.53 inch, and the length of the wider portion of the case has a ratio to such outer case diameter of no more than about 3.33.